Fluorescence is generally understood to be a property that enables certain materials to absorb light energy and radiate visible light at a longer wavelength than the absorbed light. Without being limited to any specific theory, it is widely accepted that electrons in fluorescent materials are excited upon being illuminated by light energy of a specific wavelength, and light energy of a longer wavelength is radiated from these materials as the electrons return to the unexcited or ground state. The specific excitation and radiation wavelengths are characteristics of particular fluorescent materials. The apparent brightness of a fluorescent material's luminescence is dependent, among other factors, on the wavelength emitted by the material and the intensity of the incident radiation that excites the material. A fluorescent material that has its excitation peak at a specific wavelength may quickly emit a much reduced luminescence as the wavelength of incident light deviates from the excitation peak. A fluorescent material will also lose the ability to fluoresce when the incident light does not have enough energy within the specific excitation range.
Lamps emitting radiation that excites fluorescence have been used for a wide variety of purposes, including, but not limited to, forensic inspection, readmission control, counterfeit currency detection, contamination inspection, non-destructive testing, and leak detection on equipment such as air conditioning and other fluid-containing systems. The lamplight is commonly in the ultraviolet (UV) or in the visible blue-violet range, exciting a fluorescence somewhere in the visible range. The fluorescent material may be deliberately provided. For example, some banknotes have a fluorescent marker embedded in the paper and the UV light is used to detect the otherwise hidden marker. In another example, one method for detecting leaks in an air conditioning system is through the use of fluorescent dyes that are added to and mixed with the refrigerant in the system, with the combination of refrigerant and dye circulating through the air conditioning system. This method was first pioneered by Spectronics Corporation, the assignee of the present invention. In these leak detection systems, the dye circulates through the system, eventually seeping out at the source of the leak. When exposed to a suitable light source, such as an ultraviolet (UV) light, the dye fluoresces, thus highlighting the source of the leak. Ink that is visible only by fluorescence under an ultraviolet lamp can also be used in re-admission stamps at entertainment events.
The fluorescence may be an incidental property of some material that it is desired to detect, measure, or observe. For example, many biological materials, including rodent hair and urine, are naturally fluorescent. Other examples of the use of fluorescence include the detection of counterfeit currency and other documents. Many minerals, such as diamonds, can be recognized or distinguished by their levels and colors of natural fluorescence.
Many current fluorescence-exciting lamps emit light in long wave ultraviolet (UV-A) wavelength range of about 320 nm to about 400 nm, for example, around 365 nm, in the medium wave ultraviolet (UV-B) range from about 280 nm to about 320 nm, for example, around 315 nm, or in the short wave ultraviolet (UV-C) range, for example, around 254 nm, or in the visible violet/blue range from about 400 nm to about 480 nm within the electromagnetic spectrum.
Unfortunately, visible (including ambient) light competes with the fluorescence from dye for the attention of the person conducting the test. The visibility of the fluorescent response is increased when the intensity of other visible light is reduced, so that the fluorescent response is not masked or washed-out by other light. This is particularly true where the system has shiny surfaces that reflect visible or ambient light. Thus, ultraviolet lamps directed in otherwise dark conditions at a system containing a UV responsive fluorescent material may reveal the fluorescent material glowing against the dark background. When performed in total darkness, the outcome of such a procedure is often enhanced; however, total darkness is often not available in testing environments, such as an outdoor air conditioner where the sun cannot be shut off, or a shop floor where darkness may be dangerous when machinery in motion is involved.
Similarly, luminescent materials are also used in non-destructive testing. For example, fluorescent dyes combined with iron filings can be used to detect faults such as stress fractures. The combination of iron filings and fluorescent dye is attracted to the faults and, again, the dye emits visible light when illuminated by appropriate incident wavelength light. A very small fault is often difficult to detect even though such a small fault may present a potentially great danger. Thus, any assistance in identifying these faults would be beneficial.
Existing ultraviolet lamps have several weaknesses. Some concerns with existing ultraviolet lamps are their cost, size, and power consumption. For low power consumption and cost, fluorescent lamps can be used to generate the incident radiation. However, fluorescent lamps generate a low intensity of incident ultraviolet radiation. Because of this, it is desirable to be able to bring the lamp in close proximity to the fault. This is often difficult in the tight spaces available when working around machinery and equipment.
A hand-held UV lamp was developed by Spectronics Corporation and is described in U.S. Pat. No. 6,953,940, which is incorporated herein by reference in its entirety. That lamp is light and easily maneuverable. However, the small area of illumination generated by the lamp makes inspection of larger areas more time consuming. More particularly, the narrow width of the unit permits light from the surrounding environment to sometimes overpower the fluorescent response in brightly lit rooms, thus making detection difficult. The narrow width of light also has limited usage in the field of non-destructive testing where typically large areas are being tested for faults.
Halide lamps are currently in common use in non-destructive testing (NDT), but halide lamps get very hot and project light covering a wide wavelength. To accommodate for the wide wavelength coverage, expensive filters are used to remove the unneeded wavelengths of light and project the proper wavelength needed for testing. Since the filters are absorbing or reflecting light, they tend to heat up the ambient air surrounding the lamp.
A need, therefore, exists for a lamp head that is compact, emits ultraviolet (including blue wavelength) light with an effective intensity, and does not generate a large amount of heat.